Photochemical nitrogen elimination of 1,2,3‐thiadiazoles leads to primary fragments (1, X = S), which are able to cyclize to thiirenes (2, X = S). An exception is found for bicyclic systems like 4. These results, gained by isotope labelling experiments are related to the oxirene formation of α‐oxocarbenes.

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Hydrogen diffusion / Aluminium / ElectrochemistryThe growing interest on hydrogen in aluminium based materials is directed in finding solutions for hydrogen induced corrosion problems. Although the corrosion mechanism is not yet understood totally it is uncontested that it arises from mechanical stress inside the material caused by hydrogen diffusion into the bulk.On this background it is of technological interest to study the diffusion and solubility behaviour of hydrogen in aluminium and aluminium alloys. The hydrogen diffusion measurements were performed by applying the potentiostatic and galvanostatic permeation and the current pulse method using the electrochemical double cell technique. A precondition of application of these permeation techniques is the complete absence of hydrogen impermeable oxide layers and the exclusion of corrosion by the electrolyte. For these reasons the natural oxide layers on aluminium and its alloys were removed by ion sputtering. Reoxidation and direct contact with the electrolyte were avoided by coating the cleaned surface with an only hydrogen permeable palladium film. Due to the solubility of aluminium oxide/hydroxide in aqueous solutions, which leads to a permanent oxidation of the sample, to a hydrogen evolution and even to an exfoliation of the palladium film, high denseness of this film was required. For this reason relatively thick (5 gm) protecting films had to be used at first. On the other hand, this results in a multilayer problem and therefore, in combination with the low hydrogen solubility of aluminium, in difficulties in the determination of the diffusion and solubility. A way to avoid these problems was the use of formamide as non-aqueous, non-oxidizing, but protic solvent for the electrolyte solution.

Bei der Photolyse der Titelverbindungen 1 a -d werden Heterocyclen der Typen 1 ,4-Dithiin 5, 1,3-Dithiol9, Thiophen 11 und 1,2,4,5-Tetrathian 12 isoliert. Die Ausbeute auf den Reaktionswegen I -VI in Abhangigkeit von der Cycloalkeno-1,2,3-thiadiazol-RinggroRe ist von Interesse (Tab. 1). Photolysis of Cycloalkeno-l,2,3-thiadiazolesPhotolysis of the title compounds leads to several types of heterocycles: 1,Cdithiins 5 , 1,3-dithioles 9, thiophenes 11, and 1,2,4,5-tetrathianes 12. The yields of the reaction routes I -VI depend on the ring size of the cycloalkeno-1,2,3-thiadiazoles (table 1).